The invention relates to a blind rivet having a hollow rivet body made of plastic, which has an elongated shank that extends coaxially to a longitudinal center axis of the blind rivet and has a bore, having a head extending radially at one end of the shank for contact with an accessible side of a workpiece, and having, at the opposite end, a foot end that is passed through an opening in the workpiece, and having, located in the bore of the rivet body, a mandrel that has a mandrel shank with a drawing end projecting out of the head of the rivet body and with a mandrel head that stands in operative connection with the foot end of the rivet body in order to transmit a force to the rivet body during setting of the blind rivet.
Blind rivets are used to permanently join workpieces that are in contact with one another. The workpieces typically have holes passing through them that are brought into alignment with one another and into which the blind rivet is placed and then fastened by deformation. A fastened blind rivet results in a clearance-free seating in the holes of the workpieces and clamps the workpieces together. Normally, a blind rivet is never removed again. However, in cases in which repair of the joined parts is necessary or when a blind rivet has been set incorrectly, it is necessary to remove a blind rivet.
In the automotive industry, uses of blind rivets include fastening door module supports that are populated with attached parts such as power-window motors, loudspeakers, and other parts if applicable, to the door frame using multiple blind rivets. Failures of individual attached parts can make it necessary for doors to be disassembled and the door module supports to be removed. The blind rivets previously used must be drilled out for the disassembly. During this process, wandering of the drill can occur when the rivet mandrel is made of a relatively hard material, such as steel, and the rivet body is made of a relatively soft material, such as aluminum. Thus it is not uncommon for the door frame and also the module support to be damaged during the drilling-out process. The drilling chips and removed parts of the rivet fall to the ground or even into the blind area of the door, and can only be removed from the latter with extra effort. There is thus a need to create a blind rivet for these and other applications which can be released in a simple manner and can be removed in a single piece. In addition, the blind rivet must be simple to install and must join the workpieces firmly and permanently to one another after assembly.
A blind rivet that is intended to be removed in a single piece is known from EP 1 728 569 A1. In this blind rivet, which has a rivet body with a head designed as a flange and has a rivet mandrel passing through the rivet body, the rivet mandrel is shaped such that it can be pulled at least partially through the rivet body and out of the end of the rivet body opposite the flange during setting of the blind rivet. In addition, the flange is provided with a stepped region for the placement of a rivet removal tool, with the flange being dimensioned such that it does not deform or break when the rivet is withdrawn. In this blind rivet, the rivet body is made of plastically deformable metal and is dimensioned such that it projects only a short distance on the blind side of the workpieces. Accordingly, setting of the rivet forms only a comparatively small bead, which can be pressed together by a tensile force acting on the rivet body, in order to thus allow the blind rivet to be pulled from the holes in the workpieces. However, it is disadvantageous here that the holding forces of the blind rivet are very limited, and, like the release forces, are strongly dependent on manufacturing-related dimensional variations in the holes and the rivet parts.
In addition, from DE 29 06 250 A1 is known a plastic blind rivet with a mandrel having an expanded head and a rivet body surrounding the mandrel, in which the mandrel has a series of engagement teeth on its outer circumference, and the wall surface of the rivet body has a series of anchor steps suitable for engaging the engagement teeth. The rivet body is provided with a flange-like head part and with an end that is inseparably joined to the mandrel head, and is deformed during setting of the blind rivet by partial withdrawal of the mandrel from the rivet body such that a part of the wall surface of the rivet body adjacent to the mandrel head is folded outward around the mandrel head and, together with the mandrel head, is pulled into the other part of the wall surface, with the latter bulging outward. In this process, the folded section of the wall surface is forced in between the mandrel head and the unfolded section of the wall surface, in which process the unfolded wall section must be stretched very severely. This requires relatively high forces for setting the blind rivet and results in severe stressing of the plastic material, restricting the choice of material. The prior art plastic blind rivet is not designed for easy removal of the set blind rivet.